Year	2011 U.S. Dollars
1970-01-01	21.54
1971-01-01	22.59
1972-01-01	24.09
1973-01-01	25.52
1974-01-01	26.91
1975-01-01	27.19
1976-01-01	27.75
1977-01-01	29.07
1978-01-01	30.55
1979-01-01	31.45
1980-01-01	31.99
1981-01-01	32.71
1982-01-01	34.86
1983-01-01	35.70
1984-01-01	36.58
1985-01-01	38.05
1986-01-01	38.82
1987-01-01	39.11
1988-01-01	40.31
1989-01-01	41.66
1990-01-01	42.48
1991-01-01	43.11
1992-01-01	43.98
1993-01-01	44.57
1994-01-01	45.65
1995-01-01	46.85
1996-01-01	47.02
1997-01-01	47.99
1998-01-01	49.17
1999-01-01	49.97
2000-01-01	51.74
2001-01-01	52.24
2002-01-01	53.80
2003-01-01	54.33
2004-01-01	54.59
2005-01-01	55.43
2006-01-01	57.04
2007-01-01	57.08
2008-01-01	56.49
2009-01-01	56.17
2010-01-01	56.93
2011-01-01	57.70